1S :11570-1985 Indian Standard CRITERIAFOR HYDRAULIC DESIGN OF IRRIGATION INTAKE STRUCTURES In t a ke St r u ct u r es Sect ion a l Com m it t ee, Chairman SHRI BDC 55 Representing K. MADH AVAN Membe m Central Water Commission, New Delhi; Institution of Engineers, New Delhi and Com m on In dia Lim it ed, Bom ba y SH RI S. CH AKRABARTI SH RI S. R. MUNIP ALLI ( Alternate ) CH IE F E N GIN E E R-I ( IRRIGATION ) In st it u t e of H ydr a u lics H ydr ology, P oon di AN D DP LE CTOR ASSISTANT DIRE CTOR-I (H YDRAULICS ) ( Alternate ) Ir r iga t ion Wor ks, Gover n m en t of P u n ja b, CH IE F E NGINE E R(TH E IN DAM Ch a n diga r h DE SIGN ) DIRE CTOR (TRP ) ( Alternate ) Delh i Wa t er Su pply Un der t a kin g, N ew Delh i SH RI J . D'CRU Z SH RXS. A. SWAMY ( Alternate ) Cen t r a l Wa t er Com m ission , N ew Delh i . DIRE CTOR (H CD)-I "DE P UTY DIRE CTOR ( P H -I ) ( Alternate) Cen t r a l Water and Power Research Station, DIRE CTOR Pune SH RI V. K. KULKARNI ( Alternate MANAGING DIRE CTOR SH RI MOH E NDJ R SINGH DR A. V. NATARAJ AN ) N a du P u blic Wor ks E n gin eer in g Cor por a t ion Lt d, Ma dr a s Ir r iga t ion Depa r t m en t , Gover n m en t of Ut t a r P r a desh , Lu ckn ow Cen t r a l In la n d F ish er ies Resea r ch In st it u t e, Ba r r a ojoir e In st it u t e, of Gu ja r a t Ta m il SH R1 A. B. MUKH E RJ E E ( Alternate ) and P ower Resea r ch Ir r iga t ion SH RI"T. C. P AUL Am r it sa r Ir r iga t ion Depa r t m en t , Gover n m en t SH RI N. RAMASWAMY Ga n dh in a ga r SH RI B. J . SH AH ( Alternate ) ( Continued @ Copyright 1986 on page 2 ) 1957 ) a n d This publication r epr odu ct ion in wh ole or in pa r t by a n y m ea n s except wit h wr it t en per m ission of t h e pu blish er sh a ll be deem ed t o be a n In fr in gem en t of copyr igh t u n der t h e sa id Act . INDIAN STANDARDS INSTITUTION is protected under the Indian CopyrightAct ( XIV of IS :1 1 5 7 0 -1 9 8 5 page 1 ) Representing Cen t r ;l$oa r d of Ir r iga t ion and P ower , N ew ( Continuedfrom SE CRE TARY Members J OINT SE CRE TARY(Alternate DR H . R. SH ARMA SUP E RINTE NDINGE NGINE E R SH RI ) Cen t r a l E lect r icit y Au t h or it y, N ew Delh i Ir r iga t ion Depa r t m en t , Gover n m en t of Ma h a r a sh t r a . Na sik Na t ion a l H idr oelect r ic P ower Cor por a t ion Lim it ed, N ew Delh i Dir ect or Gen er a l, 1% (&-officio Member) N . VISVANATH AN SH RI G. RAMAN, Dir ect or (Civ E n gg) Secretary SH RI P . SATYANARAYANA Assist a n t Dir ect or (Civ E n gg), IS1 2 IS : 1 1 5 7 0- 1 9 8 5 Indian St andard CRITE RIA F OR H YDRAULIC DE SIGN OF IRRIGATION INTAKE STRUCTURE S 0. F OREWORD 0.1 This Indian Standard was adopted by the Indian Standards Institution on 6 December 1985, after the draft finalized by the Intake Structures Sectional Committee had been approved by the Civil Engineering Division Council. 0.2 An intake is provided in an irrigation development to allow water into a channel or tunnel under controlled conditions. The intake design shall be such as to: a) give minimum hydraulic losses, b) provide smooth entry into the water conductor system, and c) prevent/minimize ice, floating trash and coarse sediment entering the tunnel or channel. 0.3 For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with the IS : 2-1960". The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard. 1 . SCOPE 1 .1 This standard lays down the criteria for hydraulic design of irrigation intake structures. Typical layouts of intake structures are also covered in this standard. 2. TYPES AND CHOICE OF INTAKES 2.1 The position and location of an intake generally depend upon the t ype of in t a ke a n d may be broadly classified as under: a) Run-of the river type intakes, and b) Reservoir type intakes. 2.2 Run-of the River Type Intake 2.2.1 Run-of the river type intakes are those which draw water from the fresh continuous river inflows without any appreciable storage A typical sketch of intake to meet upstream of the diversion structure. *Ru les for r ou n din g off n u m er ica l va lu es ( r evised). 3 IS : 1 1 5 7 0- 1 9 8 5 special characteristics, such as steep slopes, high peaks and short duration flood flows and high sediment loads, is shown in Fig. 1. .RIGHf BANK RIGHT HEAD CANAL BANK WORKS FLOW r FT BANK HEAD WORKS SLUICE FLOW SLUICE GATE CREST OF DIVERSION GUIDE WALL 1B Modified Design 4 of Head Works F IG. 1 RU N -OF RIVER TYP E IN TAKE I$ : 1 1 5 7 0- 1985 2.2.1.1 Int akes adjacent t o div ersion w eir/barrage - In a run of the river type development without any diurnal pondage, an intake of irrigation water conductor system is placed upstream of diversion dam or barrage. A typical layout is shown inFig. 2. FLUSHING DESlLTlNG CANAL SLUICE X t IRRI%ATION CANAL v. STILLING BASIN AND ENERGY DISSIPATION ARRANGEMENT SECTION XX FIG. 2 TYPICAL CANAL INTAKE 2.2.1.2 Drop t y pe int ake - A diversion structure, consisting of a trench weir and trashrack structure over it, is constructed across mountain streams to entrap the entire minimum discharges of the river. The trench may be either in the river bed or in the weir (raised above the river bed) as per typical layout shown in Fig. 3 and Fig. 4. 2.3 Reservoir Type Intake 2.3.1 Reservoir type intake is provided where discharges for irrigation are drawn from storage built up for this purpose. Depending on the head, this is further categorized as under: a) Low head (up to 15 m), b) Medium head (15 to 30 m), and 4 High head (above 30 m). 5 y-OPENING GATE GROOVE ATE HANDLE FOR SINGLE FLUSHING GATE CONTROL PLATFORM N S L /-------N S ____--_-----L -----------5. FLUSHING CONDUIT -/ 3B F IG. 3 Sectional Elevation D ROP TYP E IRRIGATION IN TAKETREN CHIN RIVER B ED ENCH WEIR (TRASH NOT SHOWNI RACK CURTAIN WALLS SLOPE 3:1 m .. = 2 7 % zi UIS RIVER BED DIS RIVER BED GATE FLUSHING EMBANKMENT SLUICE GROOVE 4A F IG. 4 General D ROP TYP E IRRIGATION IN TAKE ( TREN CH IN THE WEIR ) -:Con td A STOP LOG GATE OPERATING /-BREAST PLAlrUKh( WALI HEAD ' GATE REGULATOR CEMENT CONCRETE 1:4:8 (300mm) LEAN CONCRETE (300 mm) ~-CEMENT CONCRETE l:4% 4B L-Section Through Intake TONE PITCHING coNCRETE CEMENT CONCRETE E .. I z 3 0 I 1:4:8 I FIG. 4 4C L-Section Through Flushing Duct DROP TYPE IRRIGATION INTAKE ( TRENCH IN THE WEIR ) G E IS:11570-1985 2.3.1.1 Int ake in concret e or masonry dams - In t he case of concrete or masonry dams irrigation intake structure can be located either at the toe when operating head is low or in the body of the dam itself when operating head is medium or high. Typical layouts are shown in Fig. 5A, 5B and 5C. 2.3.1.2 Int ake in eart hen dams - When the reservoir is formed by an earthern dam, the irrigation tunnel is laid below it or in the abutment. The intake structure for such situations will be a sloping intake or tower type of intake. Typical layouts for sloping and tower type intakes are As far as possible, reinforced shown in Fig. 6A, 6B and 6C respectively. cement concrete pressurized system should be avoided in the body of the earth dam. Measures like provision of steel liners and suitable drainage downstream of core, provisions of joints for differential settlements when not founded on rock should be considered in case pressure conduits are provided under earth dams. `lop: - "ARIES FROM 1.5 :, tn ,.. i) APPROACH GEOMETRY 5A Semicircular Type Intake Structure - Contd 10 IS : 1 1 5 7 0 - 1985 BELL MOUTH `BOTTOM LINE SEWCIRCULAR TRASH RACK ii) ELEVATION FROM RECT. AR SECTION PIERS iii) PLAN 5A F IG. 5 Semicircular Type Intake Structure RES ERVOIR TYP E IRRIGATION IN TAKE S TRU CTU RESIN CON CRETE/MAS ON RY D AMS - Con td 11 AXIS OF $ OF GATE FLOW GALLERY GATE JET 9 AIR VENT + I APRON ;r) LGATE BELLMOUTH SLOT LCONDUlf 5B F IG. 5 Typical Installation in a Concrete/Masonry Dams - ContiJ RES ERVOIRTYP E IRRIGATION IN TAKE S TRU CTU RESIN CON CRETE/MAS ON RYD AMS EMERGENCY GATE AND SERVICE I- INTAKE WELL 1 I MASONRY DAM AIR VENi PIPE CONDUIT TRASH RACK 0: MAXIMUM BETWEEN D1 AND D2 INTAKE WALLA 5C F IG. 5 Typical Installation in a koncrete/Masonry Dams RES ERVOIRTYP E IRRIGATION IN TAKE S TRU CTU RESIN CON CRETE/MAS ON RY D AMS `i OF MAIN r1RAS.H MAIN FINAL INTAKE SHAFT RACK INTAKE STAGE FOR OPER T VALVE CHAMBER TRASH LOW LEVEL INTAKE FOR INITIAL STAGE OPERATION (MAIN INTAKE PLUGGED) L SQUARE SECTION TRANSITION I LOCATION PLUG1 OF L MS CONDUIT CIRCULAR Frc.6A TYPICAL INSTALLATION IN AN EARTH DAM - SLOPINGINTAKE IS :11570 - 1985 TRASH RACK. 0.8 01 I rTRA8H RACK BELL MOUTH J TUNNE 1 `kTRAlGH1 LENGJH LELBOW FIG. 6B TYPICAL INS TALLATION IN AN EARTH DAM TOWER TYPE INTAKE( TYPE I ) AIR VENT PIPE `WING WALL EARTH DAM -ST . AUNC HIM6 RING I /CONDUIT WALL r L INTAKE WALL D = Maximum Between D. and & FIG. 6 C TYPICAL INS TALLATIONIN AN EARTH DAM TOWER TYPE INTAKE ( TYPE II ) 15 IS : 1 1 5 7 0 - 1 9 8 5 2 .3 .1 .3 Int ake in reserv oir independent of dam - In case of a highhead installation; irrigation tunnel taking off from a storage reservoir, the intake is located at a distance from the dam. The intake structure of such a layout will be either tower type semicircular, circular, rectangular or inclined. 3 . LAYOUT OF INTAKE STRUCTURE 3.1 Main components of an irrigation intake structure are listed below: a) Trashrack and supporting structures; b) Anti-vortex devices; c) Bell-mouth entrance with transition and rectangular to circular opening; and d) Gate slot enclosures with air vents. 3.1.1 The efficient and economic design of an intake to serve the functions set out in 0.2 will depend upon the conditions prevailing in each development. In 5.3.3 and 5.3.5 few formulae have been suggested which may be modified to suit any special condition. Hydraulic model studies may be necessary under special conditions. 3.2 The main types of layouts are given below. 3.2.1 Canal Int ake - In low-head deve!opment, the intake admits water into diversion/irrigation canal. Sediment excluder or trap is an essential component of this type of intake. The invert at inlet is generally raised to form a sill to prevent the entry of coarse fraction ofbedload into the canal. A skimmer wall to prevent the floating material and trashrack to check entry of submerged heavy bodies, such as tree trunks, are provided at the entrance. Stilling basin and energy dissipation devices on the downstream of intake, as shown in Fig. 2, are also required. In the case of trench provided either in the river bed or in the weir, desilting basin is located in the canal and the sediment entrapped is removed either manually or by flushing sluices. In some situations desilting tunnels may also be provided upstream of intake (see IS : 6531-1972* and IS : 9761-19817). 3.2.2 Semicircular Ty pe of Int ake St ruct ure - In this layout, the structure supporting the rack is formed in a semicircle in plan in front of the tunnel opening so that no parts of rack fall within a radius of 1'143 B froni face of opening, where B is the width of opening of tunnel. The main features of semicircular intake structure are: a) Semicircular trashrack structure; b) Bell-mouth entrance to tunnel; *Criteria tcriteria for design of canal head regulators. for hydraulic design of hydropower intakes. 16 IS : 1 1 5 7 0 - 1 9 8 5 c) Gate slot enclosures with air vent (Typical details Fig. 5A, 5B and 5C >; and d) Transition from rectangular to circular conduit. are shown in 3.2.3 Sloping Int ake - Sloping intake is provided in an earthen dam as shown in Fig. 6A. Trashrack for the intake (made by mild steel rectangular bars) is provided at the entrance. The top and sides at the entrance are provided with bell-mouth. 3.2.4 Vert ical Int ake - Vertical intake is essentially a circular vertical shaft. The structure above it supporting the trashrack is either tower type or hemispherical cage. The main features of this layout are: Hemispherical or tower type rack supporting structure; b) Circular bell-mouth to shaft; 4 Vertical intake shaft; and 4 Right-angled bend at the base of the shaft or an elbow to join the tunnel. a> In case of tower type intake structure, flow is regulated either by a single cylinderical gate or by a number of gates in the tower or %y a separate gate in the gate shaft. In case of hemispherical intake structure, the control gate is provided in the tunnel portion only. A typical design of hemispherical vertical intake structure is shown in Fig. 6A. 4. CONDITIONS STRUCTURE FOR LOCATION AND LAYOUT OF INTAKE 4.1 Factors influencing the choice of location and layout of intake structure are: a) Type ~of development that is run-of river scheme or storage reservoir_; b) Location and type of dam/weir; c) Type of water conveyance system that is tunnel or canal; and d) Topographical features of area. 4.2 The conditions under which the various typical layouts of intake classified in 3.2.1 to 3.2.4 are adopted, are given below. 4.2.1 a) b) c) Canal Int ake - This type of layout is adopted when: reservoir is of small capacity formed by a weir or barrage; intake is to function under low heads; and the topography and geology permit straight reaches suitable such type of intake. as for 17 IS:11570-1985 42.2 Semicircular Ty pe of Int ake St ruct ure This type of layout is adopted when: a) a reservoir is formed by a concrete or masonry dam and outlet tunnel is laid in the body of the dam; b) the topography and geology permit to have almost vertical face at tunnel inlet portal; and c) the minimum water depth above the centre line of intake is more than 0'8 of the entrance height. 42.3 Sloping Ty pe of Int ake St ruct ure This type of layout is adopted when: a) the reservoir is formed by an earthen dam and tunnel is laid below it; and b) the intake is subjected to low-head variations like in run-of the river type. 42.4 Vert ical Ty pe of Int ake St ruct ure This type of layout is adopted when: a) the intake is located at a distance from upstream face of the dam; b) the reservoir is formed by an earthern dam and outlet tunnel is laid below it; and c) the intake is subjected to large head variations, resulting in complete submergence of structure. 5. HYDRAULIC DESIGN OF COMPONENTS OF INTAKE 5.1 Centre Line of Intake 5.1.1 Centre line of intake shall be located well below the minimum draw down level to prevent formation of vortices. Suitable arrangements, such as cross walls, floating grid may be provided if necessary to Cover of water over the roof of the intake prevent/minimize, vortices. for the prevention of the formation of air entraining vortices both at vertical or horizontal pipe intake may be computed for the purpose of preliminary design from the set of curves given in Fig. 7 A and 7B works the design by trial method ( see Appendix A >. For important may be checked by model studies. 5.2 Trashrack Structure 5.2.1 At entrance to canal or tunnel, where trash may create serious problem in irrigation system, a trashrack structure shall be provided in front of the enterance to the tunnel to prevent the entry of any trash. 18 VOTEX FREE LVERTICAL IYTAKE DISCHARGE He= EFFECTIVE = RES. LEVEL HEAD -LOSSES = Q 7A FIG. 7 Co-efficient of Discharge vs Unit Circulation OPTIMUMSUBMERGENCE - Con td DIAGRAMS F~RDETERMINING IS : 1 1 5 7 0 - 1 9 8 5 ' 5.2.2 The trashrack structure shall be designed IS : 1138%1985* and IS : 9761-1981t. in accordance with 5.3 BelLMouth Opening and Transition - A typical sketch is shown in Fig. 8. In non-pressurized system the gate should be provided outside the bell-mouth end. 5.3.1 S h ape n n d S ize of Open in g - Entrance to the irrigation tunnel shall be designed to produce an acceleration similar to that found in a jet issuing from a sharp edged orifice. The surface shall be formed to natural contraction curve and the tunnel assumed to the size of orifice jet at its maximum contraction. 5.3.2 The normal contraction with coefficient of contraction C, as 0'6 shall be used in high-head inhtaliations and Ce as 0'7 for low-head installations in order to reduce the height of opening. Coefficients of discharge and loss coefficients for typical entrances for conduits are given in Table 1. OF TUNNEL 8A FIG. 8 Elevation Con td BELL-MOUTH DETAILS OF RECTANGULAR OPENING 1 *Recommendations for design of trashracks for intakes. TCriteria for hydraulic design of hydropower intakes. 21 IS : 11570 - 1985 -*--_=I a2' %f 8B FIG. 8 Plan BELL-MOUTH DETAILS OF RECTANGULAR OPENING TABLE 1 COEFFICIENT OF DIS CHARGE AND LOSS COEFFICIENTS CONDUIT ENTRANCES COEFFICIENT A &axiMiniAver? mum mum age 0.70 0.60 0.63 0.81 0.95 0'85 0.92 0.96 0.68 0.71 0.77 0.79 0.88 0.70 0.82 0.82 0.90 0.95 FOR a) Gate in thin wall unsuppressed contraction Loss COEFFICIENT ---Y MaxiMini- Avermum mum age 1.80 l-00 l-50 1 .2 0 1 .oo 070 0.60 0.27 0 .5 0 0.10 0.40 0.18 0.08 1.00 0.50 0.50 0.23 0.10 b) Gate in thin wall-bottom and sides suppressed cl Gate in thin wall-corners rounded entrances d) Square-cornered e) Slightly rounded entrances f) Fully rounded entrances h) Square bell-mouth entrances j) Inward projecting entrances f3) Circular bell-mouth entrances 0.98 0.97 0'80 0.95 0.91 0'72 0.98 0.93 0.75 0.10 0.20 0.93 0.04 0.07 0.56 005 0.16 0.80 22 IS : 1 1 5 7 0 - 1 9 8 5 5.3.3 O pening Area Opening area = where 4 =a2dgle of inclinationof Conduit area ce cos + centre line of conduit to horizontal, as defined in 53.2. Ce = Coefficient of contraction 5.3.4 Ent rance Curv es for Circular Conduit s - For circular conduits, an elliptical entrance curve obtained from the following equation will satisfy the streamlining requirements: where X and Y are coordinates measured parallel to and prependicular to the conduit centre line respectively, and D is the diameter of the conduit. 53.5 Ent rance Curv es for Rect angular 5.3.5.1 Height and w idt h of opening Conduit The height is calculated by the distance above and below the intersection of the tunnel centre line with the face of the entrance ( see Fig .8)*. Centre line to upper edge: (1'21 t a n 2+t 0'0847)~ Centre line to lower edge: hz = D 3 I( h, = hl + h, + 0'077 t a n 4 + &1'10 t a n 4 1 >I 5.3.5.2 Shape of t he opening - For a rectangular entrance with the invert at the same elevation as the upstream floor and with curved guide piers at each side of the entrance openings, both the bottom and side contraction will be suppressed and a sharper contraction will take place at the top of the opening. For this condition, the top contraction curve is defined by the equation: g2+ (0.sY7ZH,2 =' where His the vertical height of the conduit entrance shape. 23 downstream from the IS :11570 - 1985 For rectangular or square openings g+ ( **ZD )2 = l where D is the vertical height of the conduit for defining top and bottom curves and is the horizontal width of the conduit for defining side curves. The above mentioned formulae for rectangular/square conduit are .applicable when the centre line of the transition and centre line of conduit are the same. For higher heads shape of the opening may be decided by model studies. 5.3.6 Transitions - In order to obtain most economical design of intake transitions from a rectangular section to a circular conduit, the vertical walls are flared in the direction of flow. The transition shall be designed in accordance with the following requirements: 4 Transition or turns shall be made about the centre line of mass flow; b) For contraction, the maximum convergent angle should not exceed that indicated by the relation: tan where cy = Angle of the conduit centre line, U 2 An arbitrary parameter wall surfaces V = d/g-, with respect to its a = r u and H = Vertical height of the conduit. The-value of V and Hare the average of the velocilies at the beginning and end of the transition. 1 For expansion tan (Y= 2~ and dimensions For usual installations, the flare angle should not normally exceed 10". c) The area of any section of the transition shall be proportional to the area of a jet at similar section and modified to provide the acceleration necessary to turn the water through the angle that section makes withthe face, and d) All slots or other necessary departures shall be outside the transition zone. 24 from the neat outline IS : 11570 - 19855 5.4 Intake Gates and Air Vent 54.1 The intake gate slot shall be enclosed in a structure designed t@ guide the water into the rectangular opening without side contraction. 5.4.2 The upstream edge of the gate slot shall be at least 0'40 &from the nose, where be is the width of opening. 5.43 Where gates are located in a gate shaft, suitable transition from circular to rectangular gate slot shall be provided. 5.4.4 Siz e of Air Vent - An air vent is provided just downstream of the gate to prevent occurrence of excessive subatmospheric pressure. The air vent shall be so designed as to admit air with velocity not exceeding 50 m/s. The area of air vent is given by value of air demand divided by the maximum permissible velocity. Air demand shall be computed on the considerations of type of flow occurring downstream of gates, namely, spray flow, free flow, foamy flow, hydraulic jump formation with free surface flow or hydraulic jump formation with pipe flow. The air demand for different flow types in the conduit shall be computed with the help of the following formulae: a) For hydraulic jump formation, B = 0'006 6 ( FIG - 1 )le4 where B is the ratio of volume flow rate of air to that of water, a& Kc is the Froude number at vena contracta; b) For Spray flow, P = 0'2 FIG; and c) For free flow P = 0'09 FIG where Q8 = air demand, Qw = discharge of water, and FIG = Froude number at vena contracta. For hydraulic jump formation with channel flow and various types. of flows mentioned above, Fig. 9 may be used to compute air demand. 5.4.4.1 Prev ent ion of air-blow s - The air-blows or return blows characterised by flow of air-water mixture, more or less in the form ofa geyser, have been observed at intakes similar to those shown in Fig. 6A and 6B. Sometimes these blows may be very violent and may fn some cases the trashrack may be result in blowing of t&e trashrack. lifted and drawn in the tunnel itself. Return blows &lay be prevented by the followiflg measures: a) By providing larger open area of the trashrack; 25 IS:11570 - 1985 b) By providing another air-vent afte; the vertical bend outlet conduit; and c) By washing away the air pockets frequently by releasing discharge in the tunnel. in the higher 5.4.4.2 H ead losses in air ven t - Head loss in the air vent, specially in case of an unusually complicated vent layout containing a number of sharp bends and obstructions, shall be checked to determine whether the pressure drop exceeds 2 m of water in which case the vent size shall be increased suitably. 5.5 Approach Apron 5.5.1 The approach apron shall not be placed closer than 30 percent of the intake height, he, from the lower edge of the intake orifice. 50 LO 30 "a I8 10 5 6 3 * 6 2 1 1 2 3 L, s 7 10 20 30 a 50 70 100 (AC/A~)xt00 - Ac = Area of Flow at the Vena Contracta AT = Area of the Gutlet Tunnel FIc = Froude's Number at Vena Contracta FIG. 9 AIR DEMAND CURVESFORSPRAY,FREEAND FOAMYFLOW 26 IS : 1 1 5 7 0 - 1 9 8 5 6. MISCELLANEOUS ARaANGEMENT 6.1 For intakes provided at high altitude above snow line, necessary provision for arresting the formation of ice cover on rack bars and gate shall be made for the free flow. The proposed de-icing arrangements shall conform to IS : 10021-1981*. 6.2 Floating ice shall be arrested by providing baffle cast intakes. ice booms or concrete be 6.3 Racking Arrangement - Regular raking arrangement shall provided for intakes where floating material is expected continuously. 6.4 Sediment Exclusion - In case of run-of-river development sediment exclusion devices such as de-silting basin or flushing ducts shall be provided. 6.5 Bypass and air vent arrangement should be provided between emergency gate and service gates. in the intake APPE NDIX ( Cla u s e 5 1 .1 ) A PROCEDURE FOR DETERMINING OPTIMUM SUBMERGENCE :OR LOCATION OF CENTRE LINE OF INTAKE In order to ascertain whether at submergence `Hs' of intake pipe of diameter D = 2~0 vortex will form at the intake or not proceed as under: From the design data, the following parameters a) Effective b) Discharge head HE, to effective head HE Hs. are known: corresponding Q, and c) Submergence of the intake - *Guidelines for de-icing system for hydraulic installations. 27 IS : 1 1 5 7 0 - 1 9 8 5 c OF INTAKE SHAFT AKE BENCti INTAKE SHAFT D= 2ro HE = Effeclive head=Res.`level-head losses up to control gate St ep I Determine coefficient of discharge, C, from C = Q/A%'2 gffE Step II At any ccnvenient distance r from the centre line of the intake, such that r/D == 3, 4, 5 or 6, compute tangential velocity, Ve from the correlation: Hs = 3'45 J'er 2 -2g ( r0 > Evaluate VRr2 Step III St ep IV Q .St ep V Enter Fig. 7A plot of Ver2/Q . _ v erms C, and examine; if this point lies above the particular curve corresponding to the adopted value of r/D, no vortex will form. If this point lies below the curve vortex will form. To determine the optimum water cover or submergence repeat to the above steps till the point corresponding to the computed values of C and Ver2/Q lies on the particular r/D curve. For the case of horizontal intake, Fig. 7B may be made use of. 28 AMENDMENT NO. 1 MAY 2013 TO IS 11570 : 1985 CRITERIA FOR HYDRAULIC DESIGN OF IRRIGATION INTAKE STRUCTURES (Page 19 and 20, Fig. 7) -- Substitute the following for the existing figure: 7A FOR VERTICAL INTAKES 1 Amendment No. 1 to IS 11570 : 1985 7B FOR HORIZONTAL INTAKES FIG. 7 DIAGRAMS FOR DETERMINING OPTIMUM SUBMERGENCE 2 Amendment No. 1 to IS 11570 : 1985 (Page 21, Fig 8) ญญ Substitute the following figure for the existing: 8A ELEVATION FIG. 8 BELL-MOUTH DETAILS OF RECTANGULAR OPENING Contd... (Page 22, Fig 8) ญญ Substitute `be' for `he' (Page 23, clause 5.3.5.1) ญญ Insert the following at the end: `Width of the opening = be = Area of opening/ he' (WRD 14) Reprography Unit, BIS, New Delhi, India 3